This invention relates to the manufacture of turbine components and more specifically, to the manufacture of a turbine rotor by a cold spraying process.
Rotors used in the steam turbines, gas turbines and jet engines typically experience a range of operating conditions along their lengths. Different operating conditions complicate the selection of both rotor materials and manufacturing processes for the rotor because materials optimized to satisfy one operating condition may not be optimal for meeting another operating condition. For example, the inlet and exhaust areas of a steam turbine rotor have different material property requirements. The high temperature inlet region typically requires a material with high creep rupture strength but only moderate toughness. The exhaust area, on the other hand, does not demand the same level of high temperature creep strength but suitable materials typically must have very high toughness because of the high loads imposed by long turbine blades used in the exhaust area. Monolithic rotors of a single chemistry cannot meet the property requirements in each of the low pressure, intermediate pressure, and high pressure stages for reasons noted above.
As a result, rotors are often constructed by assembling segments of different chemistries. For example, large steam turbines typically have a bolted construction made up of separate rotors contained in separate shells or hoods for use in different sections of the turbine. Smaller steam turbines may make use of a mid span coupling to both high and low pressure temperature components together in one shell. Rotors for gas turbines and jet engines, on the other hand, are often constructed by bolting a series of disks and shafts together. While rotors having bolted construction are widely used, they suffer from several disadvantages including increased numbers of parts, increased assembly requirements, increased length of the rotor assembly and increased balance complexity.
Another method of combining different materials in the single rotor is to weld together rotor segments formed of dissimilar materials forming what may be termed a multiple alloy rotor. However, a welded rotor construction also has disadvantages such as high investment costs for the welding equipment, additional production costs for weld preparation and welding, and long production times required to inspect and upgrade the weld and the need for post weld heat treatment. The strength of rotors having a welded construction can also be limited due to a need to maintain a low carbon content in the weld and the propensity for high numbers of small non-metallic inclusions that reduce load carrying capability.
There remains a need therefore, for providing a novel way of manufacturing a turbine rotor that will reduce material wastage, permit dissimilar materials to be incorporated into the rotor construction and reduce production time and costs associated with the manufacture of the rotor.